The present invention relates to antennas of compact dielectric resonator type, more particularly antennas of this type intended to be used in RF circuits for wireless communications, especially for the mass market.
Within the framework of the development of antennas associated with mass-market products for domestic wireless networks, antennas of the dielectric resonator type or DRA (Dielectric Resonator Antenna) exhibit interesting properties in terms of passband and radiation. Moreover, this type of antenna is perfectly suited to a use in the form of surface mounted discrete components or CMS components. Specifically, an antenna of dielectric resonator type consists essentially of a block of dielectric material of any shape which is characterized by its relative permittivity εr. As mentioned in particular in the article “Dielectric Resonator Antenna—A Review And General Design Relations For Resonant Frequency And Bandwidth” published in International Journal of Microwave and Millimeter-Wave Computer-Aided Engineering—volume 4, No. 3, pages 230–247 in 1994, the passband and the size of an antenna of dielectric resonator type are inversely proportional to the dielectric constant εr of the material constituting the resonator. Thus, the lower the dielectric constant, the more wideband is the DRA but the larger it is; conversely, the higher the dielectric constant εr of the material forming the DRA, the smaller is the size of the DRA but in this case, it exhibits a narrow passband. Thus, to be able to use antennas of this type in domestic wireless networks complying with the WLAN standard, it is necessary to find a compromise between the size of the dielectric resonator and the passband, while proposing minimum bulk allowing integration into equipment.
As regards various solutions making it possible to reduce the size of dielectric resonators, a conventionally used solution consists in exploiting the symmetry of the fields inside the resonator to define cutting planes where it is possible to apply electric or magnetic wall conditions. A solution of this type is described in particular in the article entitled “Half volume dielectric resonator antenna designs” published in Electronic Letters of 06 Nov. 1997, volume 33, No. 23 pages 1914 to 1916, By using the fact that, in the planes defined with constant x and z, the electric field inside a dielectric resonator type antenna in TEy111 mode exhibits a uniform orientation and an axis of symmetry with respect to a straight line perpendicular to this orientation, it is possible to apply the theory of images and to halve the size of the DRA by effecting a cut in the plane of symmetry and by replacing the truncated half of the DRA by an infinite electric wall, namely a metallization. One thus goes from a rectangular shape of DRA represented in FIG. 1 to the shapes represented in FIGS. 2 and 3. More specifically, the rectangular dielectric resonator type antenna of FIG. 1 exhibits dimensions a, b and 2*d that have been estimated for a dielectric of permittivity εr=12.6 operating according to the TEy111 mode at 5.25 GHz frequency and that are such that a=10 mm, b=25.8 mm and 2*d=9.6 mm. If a first electric wall is made in the plane z=0 as represented in FIG. 2, in this case the rectangular DRA exhibits dimensions b and a identical to those of the DRA of FIG. 1 but a height d that is halved. Moreover, a metallization represented by the reference 1 enables an electric wall to be made in the plane z=0, According to the embodiment of FIG. 3, a second cut can be made using the symmetry of the plane z=d, and in this case one obtains an electric wall made at x=0 by the metallization 2. Hence, the dielectric resonator exhibits dimensions equal to b/2, a, d. The size of the dielectric resonator type antenna has thus been reduced by a factor 4 with respect to its base topology.